Staphylococcus aureus has become a multifaceted threat faced in our hospitals, our nursing homes, and increasingly, in our communities. In particular, methicillin-resistant S. aureus (MRSA) has been an increasing problem in each of these venues, and resistance to other antibiotics, including varying degrees of resistance to vancomycin, is increasingly complicating management of S. aureus infections. The goal of this project is to develop epitope-specific vaccines targeting alpha toxin and the phenol-soluble modulins (PSMs), which are two critical virulence factors for S. aureus, for use in preventing S. aureus infections. Antibody neutralizing determinants will be identified in alpha toxin and the PSMs through screening of peptide sequences in vivo in the mouse model. Multiple antigenic peptides (MAPs) containing universal heterologous helper T cell epitopes or autologous helper T cell epitopes identified from alpha toxin, colinearly-linked to the neutralizing B cell determinants, will then be screened for efficacy in the murine pneumonia and cutaneous abscess challenge models employing virulent alpha toxin- and PSM-producing MRSA. Immune correlates of protection, including antibody and toxin neutralizing titer and antibody affinity, will be assessed in vitro and used to model vaccine-related efficacy in preventing morbidity and mortality from S. aureus infections in mice. Following a rigorous evaluation of vaccine safety in the murine model, MAP vaccines will be validated for immunogenicity in outbred rabbits using human use adjuvants, and the rabbit antisera will be evaluated for protective efficacy using passive transfer protocols in the mouse models of S. aureus infection, as a prelude to further clinical testing in nonhuman primates. PUBLIC HEALTH RELEVANCE: Staphylococcus aureus has become a multifaceted threat that confronts us in war and peace. It is present on the battlefield, in our hospitals, our nursing homes, and our communities, turning lesser injuries and illnesses into life-altering catastrophes. It is becoming increasingly resistant to our antibiotics, and is escaping our control measures. The goal of this project is to provide the VA, and society at large, with a new tool and a new approach for countering the human and financial burden of S. aureus infections by developing a vaccine that targets two critical virulence factors, alpha-toxin and the phenol-soluble modulins. This work may lead to a safe and effective virulence factor-specific S. aureus vaccine that could broadly benefit the veteran and non-veteran population, and may facilitate the development of other virulence factor vaccines.